Multi-resistance MRAM

Abstract

Apparatuses, systems, and methods are disclosed for magnetoresistive random access memory. A magnetic tunnel junction (MTJ) for storing data may include a reference layer. A free layer of an MTJ may be separated from a reference layer by a barrier layer. A free layer may be configured such that one or more resistance states for an MTJ correspond to one or more positions of a magnetic domain wall within the free layer. A domain stabilization layer may be coupled to a portion of a free layer, and may be configured to prevent migration of a domain wall into the portion of the free layer.

What is claimed is: 
     
       1. An apparatus comprising:
 a magnetic tunnel junction (MTJ) for storing data, the magnetic tunnel junction comprising:
 a reference layer; 
 a free layer separated from the reference layer by a barrier layer, the free layer configured such that one or more resistance states for the MTJ correspond to one or more positions of a magnetic domain wall within the free layer; and 
 a domain stabilization layer coupled to a portion of the free layer, the domain stabilization layer configured to prevent migration of the domain wall into the portion of the free layer. 
 
 
     
     
       2. The apparatus of  claim 1 , wherein the domain stabilization layer comprises an antiferromagnetic layer. 
     
     
       3. The apparatus of  claim 2 , wherein the antiferromagnetic layer is configured to induce a unidirectional magnetic anisotropy in the portion of the free layer. 
     
     
       4. The apparatus of  claim 1 , wherein the domain stabilization layer comprises a multilayer. 
     
     
       5. The apparatus of  claim 4 , wherein the multilayer comprises one or more of: a cobalt/platinum multilayer and a cobalt/palladium multilayer. 
     
     
       6. The apparatus of  claim 4 , wherein the multilayer is configured to induce a coercivity increase in the portion of the free layer. 
     
     
       7. The apparatus of  claim 1 , wherein the domain stabilization layer is configured to prevent migration of the domain wall into the portion of the free layer by stabilizing a magnetization direction for the portion of the free layer. 
     
     
       8. The apparatus of  claim 1 , further comprising a controller configured to increase the resistance state of the MTJ by applying a first write current to move the domain wall in a first direction. 
     
     
       9. The apparatus of  claim 8 , wherein the controller is further configured to decrease the resistance state of the MTJ by applying a second write current in a direction opposite to the first write current, to move the domain wall in a second direction opposite to the first direction. 
     
     
       10. The apparatus of  claim 1 , wherein the free layer comprises a nucleation region configured to form the domain wall, and an arm extending from the nucleation region, the arm comprising a plurality of pinning sites for pinning the domain wall. 
     
     
       11. The apparatus of  claim 1 , further comprising a second domain stabilization layer configured to prevent migration of the domain wall into a second portion of the free layer, wherein the free layer comprises an elongate arm comprising a plurality of pinning sites for pinning the domain wall, the portion of the free layer comprises a first end portion of the arm, and the second portion of the free layer comprises a second end portion of the arm opposite to the first end portion.